Flat glass



D. G. LouKEs E'VrAL t I3,544A37 FLAT GLASS Filed Aug. 12, 1969 3lSheets-Sheet 1 Inventors /n//J Gom/v L es u. @my Mamma:

` FLAT GLASS Filed Aug. 112, 1969 3 Sheets-Sheet 2 Inventors y IAttorneys De# l, 1970 n. G. LouKes :TAL 3,544,437

FLAT GLASS Filed Aug. 12, 1969 3 Sheets-Sheet 8 hm. WW 0,0

l A ttorneyS United States Patent O 3,544,437 FLAT GLASS David GordonLoukes, Kenwyn, 17 Broom Close, Eccleston Park, Prescot, Lancashire,England, and Glen Nightingale, 47 Rookery Lane, Rainford, Lancashire,England Continuation-impart of application Ser. No. 563,138, July 6,1966. This application Aug. 12, 1969, Ser. No. 849,467 Claims priority,application Great Britain, July 9, 1965, 29,288/ 65 The portion of theterm of the patent subsequent to Sept. 16, 1986, has been disclaimed anddedicated to the Public Int. Cl. B01d 59/42 U.S. Cl. 204-180 1 ClaimABSTRACT OF THE DISCLOSURE Float glass having a concentration of metalin a surface of the glass is produced while the ribbon of oat glass isadvanced along' a bath of molten metal. Metal migration into the glassis effected by isolating a molten body of electrically conductivematerial on the upper surface of the ribbon and passing electric currentthrough the glass between the molten body and the bath.

CROSS-REFERENCE TO RELATED APPLICATION This application is acontinuation-impart of our copending application Ser. No. 563,138 filedJuly 6, 1966, now Pat. No. 3,467,508.

BACKGROUND OF THE INVENTION This invention relates to float glass andmore especially to a new float glass product. It is a main object of thepresent invention to provide a new oat glass product which has good heatreflecting and light transmitting properties.

SUMMARY According to the invention float glass having a concentration ofmetal embodied in a surface of the glass is produced by advancing flatglass in ribbon form along a molten metal surface, confining asegregated pool of molten electrically conductive material on the uppersurface of the glass, and passing an electric current through the glassbetween the segregated pool and the molten metal surface to cause metalmigration into the glass.

The invention also comprehends sheets of glass which have been treatedindividually, and sheets of glass cut from a ribbon of float glassproduced on a bath of molten metal which ribbon is surface modified byelectrical treatment as it is advanced along the bath.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional elevation ofapparatus for producing surface modified float glass according to theinvention including a tank structure containing a bath of molten metal,a roof structure over the tank structure and apparatus for pouringmolten glass on to the bath,

FIG. 2 is a plan view of the apparatus of FIG. 1 but with the roofstructure removed,

FIG. 3 is a plan view of an edge forming tool for shaping the margins ofthe ribbon, two such tools being employed in the apparatus of FIGS. land 2,

FIG. 4 is a section on line IV--IV of FIG. 3,

FIG. 5 is a section through one margin of the ribbon of glass showingthe first stage of the shaping of that margin by the part of the toolillustrated in FIG. 4,

FIG. 6 is a section on line VI-VI of FIG. 3,

FIG. 7 is a section through the margin of the ribbon Patented Dec. 1,197O DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2of the drawings, a forehearth of a continuous glass melting furnace isindicated at 1 and a regulating tweel at 2. The forehearth ends in aspout 3 comprising a lip 4 and side jambs 5, one of which is shown inFIG. 1. The lip 4 and side jambs 5 together constitute a spout ofgenerally rectangular cross section.

The spout 3' is disposed above the floor 6 of an elongated tankstructure including side walls 7 joined together to form an integralstructure with the floor 6, an end wall 8 at the inlet end of the tank,and an end wall 9 at the outlet end of the tank. The tank structureholds a bath of molten metal 10 whose surface level is indicated at 11.The bath is, for example, a bath of molten tin or of an alloy of tin inwhich tin predominates and the bath has a specific gravity greater thanthat of glass.

A roof structure is supported over the tank structure and the roofstructure includes a roof 12, side walls 13 and integral end walls 14and 15, respectively, at the inlet and outlet ends of the bath. Theinlet end Wall 14 extends downwardly close to the surface 11 of themolten metal to define with that surface an inlet 16 which is restrictedin height and through which molten glass is advanced as will bedescribed below. The outlet end wall 15 of the roof structure defineswith the outlet end wall 9 of the tank structure an outlet 17 throughwhich the ultimate ribbon of glass produced on the bath is discharged onto driven conveyor rollers 18 mounted outside the outlet end of the tankand disposed somewhat above the level of the top of the end walls 9 ofthe tank structure so that the ribbon is lifted clear of the wall 9 fordischarge through the outlet 17.

The rollers 18 convey the ribbon of glass to an annealing lehr inwell-known manner and also apply tractive effort to the ribbon of glassto assist in advancing the ribbon as it glides along the surface of thebath 10.

An extension 19 of the roof 12 extends up to the tweel 2 and forms achamber with side walls 20 in which chamber the spout 3 is disposed.

Molten soda/lime/silica glass 21 is poured onto the bath 10 of moltenmetal from the spout 3 and the tweel 2 regulates the rate of flow of themolten glass 21 over the spout lip 4. The spout is vertically spacedfrom the surface 11 of the bath so that the molten glass 21 has a freefall of a few inches, exaggerated in FIG. l, to the bath surface. Thisfree fall is such as to ensure the formation of a heel 22 of moltenglass behind theglass 21 pouring over the spout, which heel 22 extendsup to the inlet end wall 8 of the tank structure.

The temperature of the glass as it is advanced along the bath isregulated from the inlet end down to the discharge end by thermalregulators 23 immersed in the bath 10, and thermal regulators 24 mountedin the headspace 25 which is defined over the lbath by the roofstructure. A protective gas is supplied to the headspace through ducts26 which are provided at intervals in the roof 12. The ducts 2.6 areconnected by branches 27 to a header 28'which is connected to a supplyof protective gas. Thus a plenum of protective gas is maintained in theheadspace 25 which is a substantially closed headspace "and ther'eisoutward ow of protective gas through the inlet 16 and the outlet 17.

The temperature of the molten glass is regulated by the thermalregulators 23 and 24 as the glass is advanced along the bath so as toensure that a layer of molten glass 29 is established on the bath. Thislayer 29 is advanced along the bath through the inlet 16 and as it isadvanced there is free lateral ow of the molten glass under theinfluence of surface tension and gravity until there is developed fromthe layer 29 a buoyant body 30 of molten glass, which is then advancedin ribbon form along the bath.

The width of the tank structure at the surface level 11 of the bath isgreater than the width of the buoyant body I30 of molten glass so thatthere is no limitation to the initial free lateral flow of the moltenglass.

The margins of the ribbon are shaped as it is further advanced to formthe ribbon into a shallow trough or Vchannel in order that moltenelectrically conductive material may be contained laterally on the uppersurface of the ribbon of glass and completely isolated from the moltenmetal bath. One way of shaping the margins of the ribbon of glass toproduce the shallow channel is illustrated diagra-mmatically in FIGS. 1and 2 and in greater detail with reference to FIGS. 3 to 8. Two edgeforming tools 31 and 32 of a material which is not wetted by moltenglass, for example carbon in the form of graphite, are mounted atopposite sides of the tank structure.

The tools may be water-cooled if desired and are partially immersed inthe molten metal of the bath, as shown in FIG. 1.

The tools have specially shaped forming surfaces for engagement by themargins of the ribbon of glass. The tools are a mirror image of eachother and a plan view of the tools 31 is shown in FIG. 3. The shape ofthe forming surface of the tool gradually changes from an upward slope33 as illustrated in FIG. 4 to an inward directed curve as shown at 34in FIG. 6.

Asthe buoyant body of molten glass 30 is advanced in ribbon formthemargins of the ribbon first ride onto the upwardly sloping parts 33 ofthe tools 31 and 32 and are bent to the formation shown in FIG. whichillustrates one margin 35 of the ribbon of glass having an` upward slopematching the initialA slope 33 of the tool. Thereafter the slope 33 ofeach tool gradually curls over to assume the shape shown at 34 so thatthe margins 35 of the ribbon are both gradually folded up and over asthe ribbon is advanced, and by the time the margins of the ribbon passbeyond the downstream ends of the tools 31 and 32 they have collapsed tothe folded formation shown at 36 in FIG. 8. This folded formationtherefore produces marginal ridges along both edges of the ribbon whichgive to the ribbon a shallow trough-like configuration which enablesmolten material to be confined on the top surface of the ribbon of glass37 as it is advanced along the bath of molten metal. The height of themarginal ridge 36 formed along one edge of the ribbon of glass 37 isexaggerated in FIG. l for the sake of clarity.

The edge forming tools 31 and 32 are preferably cooled and a compositepipe 38 for supplying cooling water to the tool 31 and for exhaustingthe water is indicated in FIG. 3. The margins of the glass lose heat tothe forming tools so that the marginal ridges 36 which are formed aresuiciently stiiened to hold their form when the ribbon of glass 37 isadvanced downstream of the tools.

In an alternative embodiment of the invention glass may be delivered tothe bath at a controlled rate as a formed ribbon of glass which isadvanced onto the bath from casting rollers associated Wtih the inlet 16to the bath. The casting rollers both deliver glass in ribbon form tothe bath and advance the ribbon along the bath towards the outlet endthereof. The casting process for delivering a formed ribbon of glass tothe bath may be elaborated by `forming marginal ridges on the ribbon ofglass before it is delivered `to the bath.

The present invention is concerned wtih surface treatment of the ribbonof glass as it is advanced along the Ysurface of the bath of moltenmetal in order to impart desired surface characteristics to the glass.Near the outlet end of the 'bath where the temperature of the glass isin the region of 750 to 600 C. a body of molten electrically conductivematerial 39, e.g., a pool of molten metal, is confined on the topsurface of the glass. The sides of the pool 39 are contained laterallyby the marginal ridges 36 and forward movement of the downstream edge 40of the pool with the glass is inhibited by the upward slope of theribbon of glass as it is lifted from the bath surface for dischargethrough the outlet 17. Y In the embodiment of FIGS. l and 2 the quantityof molten material in the pool 39 is such that the pool finds its ownequilibrium thickness on the top surface of the glass, which in the caseof molten tin or a molten tin alloy in which tin predominates is about1A inch, and the upstream edge 41 of the pool remains stationaryrelative to the tank structure as the ribbon of glass is advancedunderneath the pool.

The material 39 may be a pool of molten tin or a pool of a molten tinalloy for example an alloy of tin with lithium, sodium, potassium, zinc,magnesium, aluminium, silicon, titanium, manganese, chromium or iron.Alternatively, the alloy may be an alloy of tin with one of the rareearth metals.

The upstream edge 41 of the pool 39 may be held, for example, by acarbon barrier extending across the ribbon surface just above thesurface but without touching the surface. This barrier prevents themolten material 39 from owing along the ribbon surface contrary to thedirection of movement of the ribbon, and the gap between the bottom ofthe carbon barrier and the surface of the glass is so small that surfacetension prevents the molten material from escaping through the gap.

Other ways may be employed for confining the pool of molten material onthe ribbon surface, for example, the edges of the ribbon may be raisedon carbon skids which are held in the bath surface at thexsides of thebath so that the production of marginal ridges 36 would not benecessary.

An electrode 42 carried on a conducting support rod 43 dips into thesurface of the pool 39 of molten material. The electrode 43 may be acarbon electrode or an osmium tipped copper electrode. The rod 43 passesthrough the side wall 7 of the tank structure and has a terminal 44 ixedto it. A second electrode 45 is similarly mounted on a connecting rod 46which is shorter than the rod 43 and ends in a terminal 47. Theelectrode 45 dips into the molten metal bath alongside that part of theribbon on which the pool 39 is confined. The support rods 43 and 46 areinsulated from the tank structure.

The lateral containing of the sides of the pool 39 obviates anypossibility of short-circuiting between the confined pool and the bathof molten metal and through the .electrodes 42 and 45 electrical contactis made'with that part of the upper surface of the ribbon of glass whichis supporting the pool 39 of molten material, and with the whole of thebottom surface of the ribbon of glass supported on the bath of moltenmetal. The terminals 44 and 47 are connected to a direct current supplyin such manner that the pool of molten tin 39 on the glass acts as ananode and the moltenhmetal bath 10 acts as a cathode.

A direct current of, for example, 50 amps. at a voltage of the order of50 volts is provided by the supply circuit and this` current passingthrough the thickness of the glass causes tin to migrate,electrolytcally from the pool 39 into the top surface of the` ribbon ofglass. The current which is passed through the ribbon in order toproduce a desired change in the surface characteristics of thetopvsurface depends on the speed, in square inches per second, at whichthe ribbon of glass is being advanced. The amount of tin which enters agiven square inch of the top surface of the glass depends also on thetemperature and thickness of the glass and the applied voltage.

In one method of operating, the length of the pool 39 is such that theribbon of glass takes about 60 seconds to pass under the confined poolof tin, the resulting surface concentration of tin in the top surface ofthe ribbon which is achieved being such that the ribbon taken from thebath has something of a metallic appearance.

The treated glass which is thus produced has unusual heat reflecting andlight transmitting properties and is not easily wetted by water, as Wellas having special chemical properties. After the ribbon of glass hasbeen annealed, the margins are trimmed off leaving a ribbon of fiatglass having the desired surface characteristics.

The amount of tin migrating into the surface of the glass may be in theregion of l milligram of tin per square inch of the glass surface, andwith such a concentration of tin in the surface the glass noticeablytransmits less light. If a yet higher current is passed through theglass there is a resulting surface concentration of tin in the glass inthe region of several milligrams of tin per square inch and anirridescent grey surface is produced.

I'he arrangement illustrated in FIGS. 1 and 2 gives a relatively shallowsurface treatment. If a deeper surface treatment of the glass is desiredthen the method of the invention may be applied higher up the bath,Where the glass is hotter but is not `so hot-that its upper surface isaffected by the Weight of the pool of molten material acting on it.

Metal from the bath may be caused to enter the bottom surface of theribbon of glass by reversing the electrical connections to the terminals44 and 47. The molten metal bath then acts as an anode and the pool 39of molten metal acts as a cathode, and the bath metal, e.g., tin, leador bismuth is carried electrolytically into the bottom surface of theglass ribbon. The migration of metal into the glass takes place mainlyinto that part of the bottom of the ribbon which is directly underneaththe pool 39 of molten metal.

The use of tin alloys for the pool 39 has already been mentioned, and byusing different alloys other surface finishes may be obtained for theribbon of glass.

Alloys of bismuth or lead may be used for the pool 39, for example,alloys of bismuth or lead with any one of the following elements, namelylithium, sodium, zinc, magnesium, aluminium, silicon, titanium,manganese, chromium, iron, cobalt, nickel, copper, silver, gold,antimony, arsenic and indium; or with a metal of the platinum group,that is platinum, palladium, ruthenium, rhodium, osmium, or iridium; orwith a rare earth metal.

In particular alloys based on bismuth or lead can be employed forcausing a colouring element to enter the top' surface of the glass. Forexample the top surface of the glass may be stained yellow by employinga pool of silver/bismuth alloy, or may be stained grey by a pool ofnickel/bismuth alloy. A redbronze colour is btained by employing a poolof a copper/bismuth or a copper/lead alloy, especially if the topsurface of the glass has alr'eady been reduced by hydrogen present inthe headspace over the bath, or if a reducing agent has previously beenintroduced into the top surface of the glass in the manner describedherein with reference to FIGS. 9 and 10. A pool of a bismuth/ cooper/tinalloy in correct proportions may be employed to introduce both copperand tin simultaneously into the glass surface whereupon a red colour isproduced.

Elements other than the molten metal of the bath may be caused tomigrate into the bottom surface of the ribbon of glass by maintaining inthe molten bath a requisite concentration of the desired element so thatwith the bath as the anode the electrolytic action causes the element tomove from the bath in a controlled manner into the bottom surface of theribbon of glass.

A pool of electrically conductive molten salt may be confined on the topsurface of the ribbon of glass. For example a high surface concentrationof silver may be produced in the ribbon of glass by confining a layer ofa molten silver halide, for example silver chloride, on the top of theglass near the outlet end of the bath of molten metal as illustrated inFIGS. l and 2, and then passing a controlled electric current throughthe glass with the pool of silver chloride acting as the anode. Copperor zinc may be caused to migrate electrolytically into the glass from apool of a molten copper salt or a molten zinc salt confined on the uppersurface of the ribbon of glass.

In the embodiments described above direct current is employed but it hasbeen found that an alternating current may be used, for example acurrent alternating at about 1 cycle per second, to cause tin to enterpreferentially into one surface of the glass.

A heating alternating current at mains frequency may be superimposed onthe controlled direct electric current in order to cause electricalheating of the glass thereby enhancing the controlled migration of anelement into the glass surface.

FIGS. 9 and 10 illustrate a form of apparatus according to the inventionfor modifying both surfaces 0f the ribbon of glass. Two molten pools 48and 49 are separately conned on the top of the ribbon of glass beingseparated by a sufficient distance to ensure that the pools areelectrically isolated from each other. The marginal ridges 36 formed onthe ribbon of glass contain the side edges of the pools laterally andthe upstream and downstream edges of the pools are held by means ofcarbon barriers. There are two such barriers 50 and 51 holding the frontand rear edges of the pool 48, and two similar barriers S2 and 53holding the front and rear edges of the pool 49. The carbon barriers 50to 53 are individually and adjustably supported by means of struts 55between the side Walls of the tank structure. The mounting of thebarriers 50 to 53 permits both vertical and longitudinal adjustment ofthe barriers relative to the tank structure.

Associated with the pool 48 there are two electrodes 58 and 59 whichrespectively dip into the top surface of the pool 48 and into the moltenmetal bath 10 alongside the pool 48. The electrode 58 is mounted on aninsulated connecting rod 60 fixed in the tank side wall 7 and carrying aterminal `61. The electrode 59 is carried on an insulated connecting rod`62 which has a terminal 63. The terminal 63 is connected to one end ofthe secondary Winding of a transformer 64 and the terminal 61 isconnected to the other end of that secondary winding through a rectifier65. The primary winding of the transformer 64 is connected to a source66 of alternating current.

Similarly, the pool 49 has associated electrodes 67 and 68,respectively, dipping into the pool 49 and into the molten metal bath 10alongside the pool. The electrodes v67 and 68 are carried on insulatedconnecting rods 69 and 70 having terminals 71 and 72. As shown in FIG. 9the terminal 71 is connected to one end of the secondary winding of atransformer 73 and the terminal 72 is connected through a rectifier 74to the other end of that secondary winding. The primary winding of thetransformer 73 is connected to a power supply source 75. By the use ofthis method of electrical connection the pool 48 acts as an anode withrespect to the molten metal bath 10, and the pool 49 acts as a cathodewith respect to the bath 10. Thus metal will enter the top surface ofthe ribbon of glass from the pool 48 and will enter the bottom surfaceof the ribbon of glass from the bath 10 as the ribbon passes under thepool 49 so that the ultimate ribbon of glass produced has apredetermined concentration of metal in both surfaces. This method couldbe employed in a process in which the pool 48 is a pool of a lithium/tinalloy, the pool 49 is a pool of tin, and a predetermined concentrationof lithium is alloyed with the tin of the bath 10. Lithium enters bothsurfaces of the ribbon and the glass can be strengthened by subsequention exchange reactions involving the lithium ions.

In another application of the twin-pool embodiment of the invention zincis introduced into the surfaces of the glass in controlled amounts froma tin/ zinc alloy in order to improve the weathering properties of theglass.

Both the pools 48 and 49 may have the same polarity with respect to thebath in another application of the invention to a two stage treatment ofthe top surface of the glass. For example both the pools may beconnected at anodes, the first pool being of tin or an arsenic/bismuthalloy, and the second pool being of a copper/bismuth alloy or acopper/lead alloy. A reducing agent is introduced into the top surfaceof the glass from the rst; pool,- and the copper entering the glass fromthe second pool is reduced to give a red colour to the glass.

The metal alloyed with the tin, lead or bismuth may be continuallyreplenished by electrolysis from a pool of the salt of that metal whichfloats on top of the pool of molten metal. `For example the lithium in alithium/ tin alloy may be continually replenished from a pool of alithium salt which is oated on the pool of alloy.

The effect of the surface treatment of the glass may be graduated acrossthe ribbon of glass by shaping the top pool or pools of molten metal toa nonuniform width or length. For example a laterally graded top surfacetreatment of the ribbon is achieved by holding the leading edge of thepool 39 of FIGS. 1 and 2 at an angle to the direction of advance of theribbon of glass by means of a carbon barrier.

Additionally longitudinally graded top or bottom surface treatment ofthe glass may be produced by con- Y A y A s s. A Y tinuously varying theapplied voltage and hence the current flowing through the glass.

The invention thus provides an improved method of manufacturing flatglass in which the constitution of either or both surfaces of the bathcan be accurately controlled to produce a desired surface quality of theglass. The in-v vention also comprehends flat glass produced by themethod of the invention and having a predetermined surface constitution.

What is claimed is:

1. Float glass having a concentration of metal embodied in a surface ofthe glass, produced by advancing flat glass in ribbon form along amolten metal surface, confining a segregated body of molten electricallyconductive material against the upper surface of the glass, andmodifying the surface constitution of the glass by passing an electriccurrent throughV the glass between the confined molten material and themolten metal.

References Cited UNITED STATES PATENTS 3,467,508 9/ 1969 Lou'kes et ai.6-5-30 FOREIGN PATENTS 620,787 8/ 1962 Belgium 65-30 S. LEON BASHORE,Primary Examiner JOHN H. HARMAN, Assistant yExaminer U.S. Cl. X.R.

